In the usual telephone set, a ringer or bell is connected across the conductors of the line loop in series with a capacitor blocking the passage of direct current therethrough. With the line loop open-circuited, alternating current from the central office can still pass through the electromagnetic coil of the ringer by way of the series capacitor. Even though the ringing currents have a predetermined frequency, generally of about 25 Hz, the ringer may respond to oscillations or pulse trains of lower frequency such as, for example, dialing pulses generated at a cadence of about 10 Hz by another telephone set connected across the same line loop. This is inconvenient for several reasons. Thus, a subscriber mistaking the spurious rings for an incoming call may pick up the telephone handset and thereby interfere with the dialing process of the other subscriber; furthermore, the first subscriber may monitor dialing pulses of the second subscriber against the wishes of the latter.